This invention relates to a water jet propelling vessel and more particularly to an improved water injection propulsion unit for such a vessel.
One popular form of watercraft is that of the jet propulsion type. Although this type of vessel has a number of advantages, the usual construction of the jet propulsion unit can present some difficulties.
One particular problem with this type of unit is due to the fact that the jet propulsion unit is constructed with fixed dimensions. It is thus not possible to simultaneously optimize the watercraft's accelerability and maximum attainable speed under various running conditions, as each of these normally require unique and varying jet propulsion unit dimensions. Particularly, it is not possible to increase the watercraft's accelerability during periods when the vessel speed is low, nor is it possible to maximize the vessel's top attainable speed during periods when the vessel speed is high, when employing a fixed dimension jet propulsion unit. Ordinarily, a compromise is made and the jet propulsion unit constructed in such a manner so that acceptable, but not optimal, watercraft accelerability and speed are attainable under the above-discussed conditions.
The graph of FIG. 1 illustrates the relationship of thrust and hull drag with vessel speed (wherein T is thrust, V is vessel speed, R is hull drag, A is a plot for a vessel utilizing a larger nozzle outlet area, and B is a plot for a vessel utilizing a smaller nozzle outlet area) It can be seen that utilization of a larger nozzle outlet area achieves greater thrust within the low to medium speed range while utilization of a smaller nozzle outlet area achieves greater thrust, and higher speed, within the high speed range.
It is, therefore, a principle object of this invention to provide an improved water jet propelling vessel and a construction for the jet propulsion unit for use with a watercraft.
It is a further object of this invention to provide for improved performance for such a vessel operating at varying speeds.